Flipper arm is the technical term used in the subject trade as a definition for the arms that are pivotally arranged in the corners of a spreader. The flippers arms are controllable in a downwards pivoted motion so as to extend below the spreader and in the lowered position effective for guiding the spreader upon lowering towards the top side of the container, in the connection of the spreader to the container's corner fittings through connecting means fitted to the spreader. Such flipper arms are typically associated with piston/cylinder units that are supplied from a hydraulic power system that is continuously pressurized for powering the movements of the flipper arm, as well as for holding the flipper arm in position.
A typical feature in the operation of the flipper arm is that the power needed for pivoting the flipper arm between the raised rest position and the lowered operative position may be seen as moderate, whereas the external loads on the flipper arm applied from contact with the container during positioning may be considerable, and many times the size of the power that is required for pivoting the flipper arm. For reason of security, and in order to withstand such external forces that tend to move the flipper arm away from its operative position, the flipper arm's hydraulic drive means is often oversized.